> int main(void) {
>     for (;;) {
>         sleep(1);
>     }
> }
> 
> and then send it a signal? Does it then start spinning?

No, but it doesn't respond to any signal except KILL (according to
ktrace, the process does not receive the signals).

It gets stranger: this *only* happens under X: programs running on the
console behave as expected (the integer-division-by-zero dumps core on
SIGFPE).  It doesn't matter whether I run under xterm or
gnome2-terminal, and it's both keyboard-generated signals and explicit
`kill' commands from another window that disappear without trace.

<time passes>

OK, I'm making some progress in tracking this down.  Signals only
disappear when i) I'm using GNOME, and ii) my shell is NOT csh.
(Normally I use rc, of course :-), but signals also disappear with
/bin/sh.)

It seems that something in GNOME (gnome-session? metacity?) is setting
a ridiculous signal mask.  Since csh frobs with sigprocmask() itself,
it doesn't matter - provided your shell is csh.  But when a Real Shell
inherites this crazy signal mask, you get the unhelpful behaviour I'm
seeing.

More if I get any further.

Tim.